Cladding system

ABSTRACT

A composite sheet product, suitable for porcelain enameling, having an aluminous metal cladding layer on an aluminum base core alloy containing about 2 to 3% copper, up to about 0.4% manganese, and about 0.2 to 0.6% magnesium.

United States Patent [1 1 Webb [ CLADDING SYSTEM [75] Inventor: ThomasE. Webb, Richmond, Va.

[73] Assignee: Reynolds Metals Company,

Richmond, Va.

[ Notice: The portion of the term of this patent subsequent to Nov. 26,1991, has been disclaimed.

[22] Filed: May 31, 1974 [21] Appl. No.: 474,883

Related U.S. Application Data [60] Division of Ser. No. 316,177, Dec.18, 1972, Pat. No. 3,850,585, which is a continuation of Ser. No.78,276, Oct. 5, 1970, abandoned.

[52] U.S. C1 29/195; 29/1975; 117/70 C; 117/71 M; 117/75 [51] Int. Cl.B32b 15/20; A47j 27/00 [58] Field of Search 29/1975, 195 PV; 220/64;117/70 L, 71 M, 78

145] *July 8, 1975 Primary Examiner-L. Dewayne Rutledge AssistantExaminer-Arthur J. Steiner Attorney, Agent, or Fz'rmGlenn, Palmer, Lyne& Gibbs [57] ABSTRACT A composite sheet product, suitable for porcelainenameling, having an aluminous metal cladding layer on an aluminum basecore alloy containing about 2 to 3% copper, up to about 0.4% manganese,and about 0.2 to 0.6% magnesium.

13 Claims, No Drawings CLADDING SYSTEM This application is a division ofcopending application Ser. No. 316,177 filed on Dec. 18, 1972, now US.Pat. No. 3,850,585, which is a continuation of application Ser. No.78,276 filed on Oct. 5, l970, now aban doned.

The present invention relates to a composite aluminous metal article,typically in sheet form, having an outer cladding layer suitable forporcelain enameling and an adjoining core layer which is susceptible tostrengthening under thermal conditions incident to porcelainizingtreatment. The composite is adapted for such uses as making coatedaluminum utensils, including those having an interior non-stick coating,and the core and cladding layers are selected to provide improvedresistance to exfoliation and blistering.

BACKGROUND OF THE INVENTION Aluminum utensils are commonly provided witha TFE coating on their interior cooking surfaces. Porcelain enameling isused to finish the exterior surfaces of these and other products made ofclad composites. The aluminous materials used for such purposes may be acommercial grade of aluminum (lXXX series) or a high aluminum contentalloy such as 3003, either alone or as cladding on a stronger base alloyproviding greater rigidity. Two such clad composites previously used are3003 clad 7005-type alloy and H clad 7004-type alloy.

In these applications a cladding of l 100 or 3003 aluminum has beenselected primarily on the basis of its suitability for porcelainizing orTFE coating operations, while the 7004 and 7005 type alloys have beenchosen for their responsiveness to strengthening under thermalconditions incident to such operations. It has been found that theresulting combinations are less than ideal, however, because thesecladding materials are not sufficiently anodic to such core alloys toprovide electrolytic protection. Thus, in the event of a scratch orother discontinuity which allows access of corrosive food constituentsor water and other sub stances used for cleaning purposes, a form ofcorrosion may occur which tends to spread laterally along and throughthe core layer, resulting in exfoliation and blistering.

An object of the present invention is to provide an alclad compositeexhibiting improved resistance against such attack, while stillemploying conventional cladding materials adapted for porcelainenameling.

SUMMARY OF THE INVENTION It has been found that an alclad copper-bearingaluminum base core alloy provides improved results with respect tocorrosion resistance of the composite, in that such an alloy serves tolimit attack to minor pitting of a localized nature. In accordance withthe invention, the cladding layer is bonded to a base layer of an alloyconsisting essentially of aluminum, about 2 to 3% copper, up to about0.4% manganese, and about 0.2 to 0.6% magnesium by weight. This alloymay also contain the usual incidental impurities as well as minoralloying elements in customary amounts for recognized purposes,including, for example, up to about 0.8% silicon, 0.7% iron, 0.1%chromium, 0.25% zinc and 0.2% titanium.

The cladding may be applied on one or both surfaces of the base layer. Apreferred cladding alloy is 3003,

but other conventional aluminous metal cladding materials are suitable,such as aluminum and high aluminum content alloys capable of affordingelectrolytic protection, particularly those selected from the groupconsisting of type lXXX aluminum of at least 99.0% purity and alloys ofthe 3XXX series (Aluminum Association designation) containing up toabout 1.5% manganese as the principal alloying element by weight.

EXAMPLE The following example illustrates the practice of the inventionand its presently preferred embodiment:

An ingot was prepared having a core composed of a copper-bearingaluminum base alloy and having 3003 alloy cladding l07r) on both sides.then rolled to 0.102 inch gage, blanked into suitable circles, andsubjected to thermal treatment to simulate porcclainizing and TFEcoating cycles. The core composition (alloy X2036) in weight percentageswas:

0.50 max. Si

0.50 max. Fe

0.10 max. Cr

0.25 max. Zn

0.15 max. Ti

Others, each .05 max. total 0.15 max.

Balance aluminum.

For purposes of comparison, reference specimens were prepared fromconventional 3003 clad 7005-type alloy. Exfoliation tests (5-dayMASTMAASIS standard) were performed on annealed materials, and also onthose treated for 10 minutes at l,000F. and fan cooled (to simulateporcelaining) and for 15 minutes at 750F. and air cooled (to simulateTFE coating).

The conventional materials showed moderate to severe blistering both inannealed and heat treated condition.

a In contrast, the composite matrials of the present invention showedonly slight pitting (no blistering or exfoliation attack) in eithercondition.

A clad product of this sort is known commercially as Type 36 porcelainenameling sheet." its core alloy X2036 was registered with the US.Aluminum Association on Aug. I3, 1970, by the assignee of thisapplication.

Alclad X2036 alloy in the form of such porcelain enameling sheet (PE-36)is suitable for conventional fabricating operations incident to makingvarious types of cooking utensils, particularly pans and the like havinga TFE non-stick coating or a porcelain enamel coating, or both, and suchcoatings are readily applied to a cladding surface of the compositesheet. The invention embraces the clad product itself, its use in makingcooking utensils, and related method aspects of making such products andapplying such coatings.

The term alclad is used here in the accepted sense to indicate a bondedcomposite having a layer of aluminum or corrosion-resistant aluminumalloy which is anodic to the core of structurally stronger aluminumalloy it covers, thus physically and electrolytically protecting thecore alloy against corrosion.

What is claimed is:

1. In the art of making porcelain enameling sheet having a claddinglayer of aluminous metal selected from the group consisting of type [XXXaluminum of at least 99.0% purity and aluminum base alloys ofthe BXXXseries containing up to about 1.5% manganese by weight, the improvementwhich comprises bonding said cladding to a core of aluminum base alloyconsisting essentially of aluminum, 2.2 to 3.0% copper, 0.3 to 0.6%magnesium and 0. ID to 0.40% manganese by weight.

2. in the art of making cooking utensils having a TFE coating, theimprovement which comprises applying said coating on an exteriorcladding surface of a composite sheet having a core of aluminum basealloy consisting essentially of aluminum, 2.2 to 3.0% copper, 0.3 to0.6% magnesium and 0.l to 0.40% manganese by weight and a cladding layerof aluminous metal selected from the group consistingof type IXXXaluminum of at least 99.0% purity and aluminum base alloys of the 3XXXseries containing up to about 1.5% manganese by weight.

3. in the art of making cooking utensils from composite sheet materialhaving a cladding of aluminous metal selected from the group consistingof type lXXX aluminum of at least 99.0% purity and aluminum base alloysof the 3XXX series containing up to about l.5% manganese by weight and acore layer of a higher strength aluminum base alloy, the improvementwhich comprises providing composite sheet material having a core ofaluminum base alloy consisting essentially of aluminum, 2.2 to 3.0%copper, 0.3 to 0.6% magnesium and 0.l0 to 0.40% manganese by weight anda layer of said cladding on each side of the core, applying a TFEcoating on a cladding surface at one side of said sheet, and applying aporcelain enamel coating on a cladding surface at the other side of saidsheet.

4. A clad composite article having an aluminum base alloy coreconsisting essentially of aluminum, 2.2 to 3.0% copper, 0.3 to 0.6%magnesium and 0.lO-0.40% manganese by weight; and having a cladding ofaluminous metal selected from the group consisting of type lXXX aluminumof at least 99.0% purity and aluminum base alloys of the 3XXX seriescontaining up to about 1.5% manganese by weight, said cladding beinganodic to said core alloy and effective cooperatively therewith to avoidexfoliation and blistering.

5. An article made of sheet according to claim 4, having a TEE coatingon a cladding surface of said sheet.

6. An article made of sheet according to claim 4, having a porcelainenamel coating on a cladding surface of said sheet.

7. An article made of sheet according to claim 4, wherein said sheet isclad on both sides, said article 4 having a porcelain enamel coating ona cladding surface at one side of said sheet and TFE coating on acladding surface at the other side of said sheet.

8. An article comprising a clad composite suitable for porcelainenameling, having a cladding layer of aluminous metal selected from thegroup consisting of type lXXX aluminum of at least 99.0% purity andaluminum base alloys of the 3XXX series containing up to about 1.5%manganese by weight, and an adjoining core layer of an alloy consistingessentially of aluminum, about 2 to 3% copper, up to about 0.4%manganese and about 0.2 to 0.6% magnesium. by weight, with incidentalelements and impurities not exceeding 0.8% silicon, 0.7% iron, 0.l%chromium, 0.25% zinc and 0.2% titanium.

9. The article of claim 8 wherein said core alloy contains about0.l00.40% manganese, about 0.30-0.6% magnesium and about 22-30% copper.

[0. The article of claim 9 wherein said core alloy includes incidentalamounts of silicon and iron not exceeding 0.5% each. 7

11. The article of claim 10 in the form of sheet.

12. The article of claim 8 in the form ofsheet, having a layer of saidcladding on each side of the sheet.

13. In an article of the type having an outer cladding layer suitablefor porcelain enameling and TFE coating operations, and an adjoiningcore layer of a higher strength aluminum base alloy, the improvementwherein:

a. said core layer is composed of an alloy consisting essentially ofaluminum, about 2 to 3% copper, up to about 0.4% manganese and about 0.2to 0.6%

magnesium, by weight, with incidental ,elements and impurities notexceeding 0.8% silicon, 0.7% iron, 01% chromium, 0.25% zinc and 0 .2%tita nium;

b. said cladding layer being composed of aluminous metal selected fromthe group consisting of type lXXX aluminum of at least 99.0% purity andaluminum base alloys of the 3XXX series effective to provideelectrolytic protection of the core;

0. said cladding and core in combination affording a composite articleadapted for porcelainizing treat ment at l,000F.;

d. said article being further characterized by the responsiveness of itscore alloy to strengthening under thermal conditions incident to suchtreatment and by the effectiveness of said composite in avoidingexfoliation and blistering.

1. IN THE ART OF MAKING PORCELAIN ENAMELING SHEET HAVING A CLADDINGLAYER OF ALUMINOUS METAL SELECTED FROM THE GROUP CONSISTING OF TYPE 1XXXALUMINUM OF AT LEAST 99.0% PURITY AND ALUMINUM BASE ALLOYS OF THE 3XXXSERIES CONTAINING UP TO ABOUT 1.5% MANGANESE BY WEIGHT THE IMPROVEMENTWHICH COMPRISES BONDING SAID CLADDING TO A CORE OF ALUMINUM BASE ALLOYCONSISTING ESSENTIALLY OF ALUMINUM, 2.2 TO 3.0% COPPER, 0.3 TO 0.6%MAGNESIUM AND 0.10 TO 0.40% MANGANESE BY WEIGHT.
 2. In the art of makingcooking utensils having a TFE coating, the improvement which comprisesapplyiNg said coating on an exterior cladding surface of a compositesheet having a core of aluminum base alloy consisting essentially ofaluminum, 2.2 to 3.0% copper, 0.3 to 0.6% magnesium and 0.10 to 0.40%manganese by weight and a cladding layer of aluminous metal selectedfrom the group consisting of type 1XXX aluminum of at least 99.0% purityand aluminum base alloys of the 3XXX series containing up to about 1.5%manganese by weight.
 3. In the art of making cooking utensils fromcomposite sheet material having a cladding of aluminous metal selectedfrom the group consisting of type 1XXX aluminum of at least 99.0% purityand aluminum base alloys of the 3XXX series containing up to about 1.5%manganese by weight and a core layer of a higher strength aluminum basealloy, the improvement which comprises providing composite sheetmaterial having a core of aluminum base alloy consisting essentially ofaluminum, 2.2 to 3.0% copper, 0.3 to 0.6% magnesium and 0.10 to 0.40%manganese by weight and a layer of said cladding on each side of thecore, applying a TFE coating on a cladding surface at one side of saidsheet, and applying a porcelain enamel coating on a cladding surface atthe other side of said sheet.
 4. A clad composite article having analuminum base alloy core consisting essentially of aluminum, 2.2 to 3.0%copper, 0.3 to 0.6% magnesium and 0.10-0.40% manganese by weight; andhaving a cladding of aluminous metal selected from the group consistingof type 1XXX aluminum of at least 99.0% purity and aluminum base alloysof the 3XXX series containing up to about 1.5% manganese by weight, saidcladding being anodic to said core alloy and effective cooperativelytherewith to avoid exfoliation and blistering.
 5. An article made ofsheet according to claim 4, having a TFE coating on a cladding surfaceof said sheet.
 6. An article made of sheet according to claim 4, havinga porcelain enamel coating on a cladding surface of said sheet.
 7. Anarticle made of sheet according to claim 4, wherein said sheet is cladon both sides, said article having a porcelain enamel coating on acladding surface at one side of said sheet and a TFE coating on acladding surface at the other side of said sheet.
 8. An articlecomprising a clad composite suitable for porcelain enameling, having acladding layer of aluminous metal selected from the group consisting oftype 1XXX aluminum of at least 99.0% purity and aluminum base alloys ofthe 3XXX series containing up to about 1.5% manganese by weight, and anadjoining core layer of an alloy consisting essentially of aluminum,about 2 to 3% copper, up to about 0.4% manganese and about 0.2 to 0.6%magnesium, by weight, with incidental elements and impurities notexceeding 0.8% silicon, 0.7% iron, 0.1% chromium, 0.25% zinc and 0.2%titanium.
 9. The article of claim 8 wherein said core alloy containsabout 0.10-0.40% manganese, about 0.30-0.6% magnesium and about 2.2-3.0%copper.
 10. The article of claim 9 wherein said core alloy includesincidental amounts of silicon and iron not exceeding 0.5% each.
 11. Thearticle of claim 10 in the form of sheet.
 12. The article of claim 8 inthe form of sheet, having a layer of said cladding on each side of thesheet.
 13. In an article of the type having an outer cladding layersuitable for porcelain enameling and TFE coating operations, and anadjoining core layer of a higher strength aluminum base alloy, theimprovement wherein: a. said core layer is composed of an alloyconsisting essentially of aluminum, about 2 to 3% copper, up to about0.4% manganese and about 0.2 to 0.6% magnesium, by weight, withincidental elements and impurities not exceEding 0.8% silicon, 0.7%iron, 0.1% chromium, 0.25% zinc and 0.2% titanium; b. said claddinglayer being composed of aluminous metal selected from the groupconsisting of type 1XXX aluminum of at least 99.0% purity and aluminumbase alloys of the 3XXX series effective to provide electrolyticprotection of the core; c. said cladding and core in combinationaffording a composite article adapted for porcelainizing treatment at1,000*F.; d. said article being further characterized by theresponsiveness of its core alloy to strengthening under thermalconditions incident to such treatment and by the effectiveness of saidcomposite in avoiding exfoliation and blistering.